An ion source for on-line use with a cyclotron heavy-ion beam, such as illustrated in FIG. 1 of the drawings, also known as the Integrated Target-Ion Source, is adapted to operate in an on-line mode with the Oak Ridge Isochronous Cyclotron (ORIC). The system of FIG. 1 is based on a modified Nielsen oscillating-electron ion source that receives a desired heavy ion beam from the ORIC and provides beams of radioactive products produced by the cyclotron beam interacting with a target foil.
The ion source of FIG. 1 essentially comprises a graphite cathode 1, a tungsten filament 4 coupled to an external power supply, not shown, by a pair of conductors 2 and 3, a quartz insulator 5, a graphite anode cylinder 6, another quartz insulator 5', and a graphite cathode 13 provided with an extraction hole. Mounted in a threaded hole 14 provided in the anode cylinder wall is a porous graphite-felt catcher 7, a tubular boron nitride extension 8 provided with a support gas feed tube 12 coupled thereto, a target foil 9 and a centrally apertured, graphite retainer 10, all mounted together as a unit and fitted in the threaded hole 14. p The foil 9 also serves as an isolation between the ion source plasma and the beam line vacuum. In operation, radioactive reaction products produced by the heavy-ion beam 11 from a cyclotron, not shown, interacting with the target foil 9, recoil out of the target foil 9 and are stopped in the porous graphite-felt catcher 7. With the catcher held at approximately the temperature of the ion source (1000.degree. C.), the reaction products diffuse from the catcher into the ion source where they are ionized before extracted therefrom. The Integrated Target-Ion Source of FIG. 1 has been described in an article published in Nucl. Instra. Meth., 139, 299 (1976). The performance of the ion source of FIG. 1 has been satisfactory and indistinguishable from an operation ordinary Nielson source, but is no longer used in favor of the new design of the present invention to be described hereinbelow, which meets a need to provide an on-line ion source having an increased ionization efficiency for the more difficult to vaporize elements.